Ultrahigh-frequency electron tube



y 6, 1953 E. TOURATON ETAL 2,640,112

I ULTRAHIGH-FREQUENCY ELECTRON TUBES Filed Dec. 14, 1948 2 Sheets-Sheet l .INVENTORS EMILE TOURATON RENE' ZWOBADA BY ATTORN EY y 26, 1953 E. TOURATON ET AL ULTRAHIGH-FREQUENCY ELECTRON TUBES 2 Sheets-Sheet 2 Filed Dec. 14, 1948 INVENTORS EMILE TOURATON RENE' ZWOBADA BY:

ATTORNEY Patented May 26, 1953 ULTRAHIGH-FREQUENCY ELECTRON TUBE Emile Touraton and Ren Zwobada, Paris, France, assignors to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application December 14, 1948, Serial No. 65,104 In "France December 31, 1947 3 Claims. 1

The present invention relates to improvements to velocity modulation tubes operating at ultrahigh frequencies and particularly to such tubes used for the amplification of low leve'l si nals.

The use of velocity modulation amplifiers for low power levels is limited by the background noise. The decrease in the intensity of the electron beam extends the limit of possible operation, but does not eliminate this drawback. -The background noise in velocity modulation tubes is mainly due to potentialstinduced' into theinput cavity resonator by fluctuations of the electron beam. For a given amplification, the more the resonators are damped the weaker is the background noise.

One object of the present invention is to provide an input circuit for velocity modulation tubes in which the back round noise due to the electron beam is compensated.

According to features of the invention the input circuit comprises two modulation cavity resonators.

According to another feature of the invention the two said resonators are connected by a transmission line matched at both ends and with an appropriate transit angle.

According to another feature of the invention, the transit angle of the electro-magnetic wave travelling along the transmission line and the transit angle of the electron beam inside the said resonator, differ by 1r times anodd number.

According to another feature of thelinvention, the application of the modulation-signal is efiected by incorporating into the transmission line of the amplifier tube the catcher cavity resonator of an auxiliary amplifier whose electron beam has a much lower intensity than that of the main amplifier electron beam.

The above mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following descriptioncf embodiments of the invention taken in conjunction with the accompaying drawings, wherein:

Figs. 1 and 2 show schematically diagrams of the invention.

Fig. 3 shows schematically an amplifier tube incorporating features of the invention, and

Fig. 4 is a sectional View of a preferred embodiment of an amplifier tube according to the invention.

Referring to Fig. 1, an electron beam 1, generated by an emissive cathode.2, flows through a line 3 matohed'at both its ends with resistances 4 and 5 equal to its characteristic impedance R.

After flowing through openings 6 and 1 provided in line 3, the electron beam. flows through a catcher space constituted by a cavity resonator 8 and finally reaches a collector electrode 9. It will be understood that the elements indicated by reference numerals 3 to I are only schematically represented, and actually these elements may consist of a pair of intercoupled electron bunching cavity resonators with the effective electrical length of the coupling between the bunching spaces of the resonators equal to the length of line 3 between openings 6 and 1. It is known in the art to couple such resonators by a transmission line terminated in its characteristic impedance at both ends, as is indicated by the resistances 4 and 5. The form that the cavity resonator structure may take will be described in connection with Figs. 3 and 4.

There is given below a calculation of the modulating potential Un due to the background noise generated by the electron beam after it flows through the line 3 at openings 6 and 1, in the case where the gain of the system, considered as a signal amplifier, is nil.

Let In be the current component due to the background noise at a given frequency of the transmitting band of the amplifier; let a be the transit angle of the electrons in the beam when they flow between openings 6 and 1, defined by the equation in which i1 is the time taken by the electrons to flow between the openings 6 and l, and T the period of the high frequency signal travelling along line 3; let (p be the transit angle of an electro-niagnetic Wave flowing along the transmission line between. openings 6 and l and defined by the equation as reference phase the phase in opening 7, the

modulationpotential at the input of opening '6 is:

3 The modulation potential due to the feed-back over transmission line 3 is given by and the modulation potential inside the opening I by The total modulation potential due to the noise is equal to the total it may be seen in this formula that the potential Un is nil when we have simultaneously:

P in which a and b are integers. A particular solution for angles and satisfying the above equations is 0 211" and p=1r.

If Equation 2 is fulfilled, 1 is also fulfilled. If we asume, on the other hand, that at the start potential 1h applied to the line 3 at the opening 6 is maximum, the modulation due to the signal is equal to the sum of the elementary modulations which result from the action of the following potentials: the modulation potential given by a generator and applied to line 3 at opening 6 and found at opening I, with the amplitude and potential U52 from the feedback loop with a value u =u -'iw The potential resulting from the signal modulation in opening 1 has for value It is seen that for the values of (p and a, which annul the modulation potential due to the noise, the modulation potential due to the signal is also annulled. This result is however of interest since the modulation due to the signal ceases to be nil if this signal is applied at an appropriate point of the feedback loop without causing disturbances.

If the modulation signal is applied at the center point of line 3, the electron beam will be sub- Jected at 6 and 1 to two potentials of the same amplitude and phase with a time difference of one period. This signal can be applied to the amplifier tube by effectively applying at an intermediate point of the transmission line the potentials in the catcher space of an auxiliary amplifier.

This arrangement is shown on Figure 2. In this figure, as in the others, the same reference numerals have been used to designate similar parts. The main amplifier tube is similar to that shown in Fig. 1 but the transmission line 3 is modified so as to comprise a catcher cavity resonator III for an electron beam H generated by an emissive cathode I2 and modulated in a line [3 terminated by its characteristic impedance I4 and excited by a signal at its other end. The electron beam ll terminates on a collector electrode I5.

In these conditions the electron beam 1 of the main amplifier is--modulated only by the signal on beam H and by the background noise of beam ll of the auxiliary amplifier. If we assume that the gain of the auxiliary amplifier is equal to 1 for instance, the intensity A2 of the beam ll of the auxiliary amplifier can be much lower than the intensity A1 of the beam I of the main amplifier. In this way, the noise in the main amplifier tube is reduced by an amount equal to:

0::20 log 2 Fig. 3 shows a preferred embodiment incorporating features of the invention. In this figure, an emissive cathode l6 associated with a concentrating electrode l1 generates an electron beam l8 fiowing successively through a double resonator l 9 comprising two cavity resonators 20 and 2| and then through a catcher resonator 22 and finally reaches a collector electrode 23. For the sake of clarity the sources of potential have not been shown on the drawing.

A second low gain amplifier tube is provided near the main tube. This amplifier may be of any known type. It may comprise for instance an electron gun with an emissive cathode 24, a concentrating electrode 25, a modulation resonator 26, a catcher resonator 21 and a collector electrode 28 on which falls the electron beam. The catcher resonator of the auxiliary tube and the modulation resonator IQ of the main tube are connected by two coaxial lines 29 and 30. The length of these coaxial lines is such that the electro-magnetic wave which flows inside the double space resonator l9 and the electron beam inside this resonator have transit angles defined by the above Equations 1 and 2. In this way the electron beam [8 of the main amplifier tube is velocity modulated by a signal from the catcher space of the auxiliary tube which thus serves as a modulating tube for the main amplifier. The connection between the double resonator l3 and space 21 of the auxiliary tube by means of coaxial structures 29 and 30 is given by way of example. This connection can be adjustable so as to comply with the above mentioned requirements.

Fig. 4 shows by way of example an embodiment of a velocity modulation tube similar to that shown in Fig. 3. In this figure, 3| is an evacuated glass envelope, inside of which an electron gun 32 is provided with a double resonator 33 whose openings are arranged on the same axis as the electron gun, a catcher resonator 35, and a collector electrode 36 for collecting the electron beam generated by the electron gun 32.

The electron gun comprises, for instance, an emissive cathode 31 and a concentrating electrode 38 held by an insulating disc 39 which is itself fixed by means of supporting members 45. Cathode 31 is taken as the origin of potential applied to the various electrodes. The concentrating electrode 38 is brought to a negative potential with respect to the cathode. This electron gun 32 is given by way of example and it is clear that it is possible to provide other electrodes in order to improve the focussing of the electron beam.

The electron beam then flows through bunching resonator 33 which is constituted by two adjacent cavity resonators. The modulating signal is transmitted from the other resonator 40 of the auxiliary tube by means of two coaxial lines 4| and 42. The auxiliary tube'has not been shown inits entirety on the drawing, only those parts have been shown which are used for connecting the catcher resonator 40 of the tube and the double cavity resonator 33 of the main amplifier. Coaxial line 4| is sealed on the glass envelope and the inner conductor 43 is also sealed inside the outside conductor in order to ensure that the tube be airtight in spite of this connection. The coaxial conductor 42 is mounted in the same way as coaxial conductor 4|. The double space resonator 33 is brought to a high potential.

After resonator 33, a drift space is provided by means of a cylindrical electrode 34 brought to a lower potential than the potential of the resonator. The bunching of the electrons takes place inside this space. The amplified high frequency energy is picked up inside resonating volume 35 which is brought to a high potential and the electron beam collected by a collector electrode 36 of cylindrical shape, also brought to a high potential. The collector electrode 36 is held by an insulating supporting member M which is fixed inside the tube by means 46.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention.

We claim:

1. A velocity modulation electron discharge tube comprising a cathode and a collector electode defining an electron beam path therebetween, means for velocity modulating electrons in the beam having a first and a second opening at spaced points along said beam path adjacent said cathode and coupling means extending be tween said openings and having a predetermined transit angle for an electromagnetic wave traversing said coupling means differing from the transit angle of the electrons in said beam between said openings by 11' times an odd number, means communicating with said coupling means at a point electrically intermediate both said openings for introducing signal modulation of ultrahigh frequency into said velocity modu lating means; and a device mounted about said. beam path between said velocity modulating means and said collector electrode for absorbing ultrahigh frequency energy from said beam.

2. A velocity modulation electron discharge tube comprising a cathode and a collector electrode defining an electron beam path therebetween, a first and a second cavity resonator mounted about said beam path and each having an opening therealong adjacent said cathode for velocity modulating electrons in said beam, said resonators including a coupling means therebetween having an effective electrical length such that the transit angle of an electromagnetic wave traversing said coupling means and that of the electrons in said beam between said resonators differs by W times an odd number, means cominunicating with said resonators at a distance from both said openings for introducing signal modulation of ultrahigh frequency into said resonators, and a third resonator mounted about said beam path between said first-mentioned resonators and said collector electrode for absorbing ultrahigh frequency energy from said beam, said signal introducing means comprising an additional cathode and another electrode defining an electron beam path therebetween and an additional. cavity resonator mounted about said. last named beam path for absorbing ultrahigh frequency energy from velocity modulations of said beam, said additional cavity resonator being coupled to said first and second resonators at points thereof at substantially equal electrical distances from the respective openings thereof, the intensity of the beam from said additional cathode being less than that of the beam from said first-mentioned cathode.

3. A velocity modulation electron discharge tube comprising a cathode and a collector electrode defining an electron beam path therebetween, a first and a second cavity resonator mounted about said beam path and each having an opening therealong adjacent said cathode for velocity modulating electrons in said beam, said resonators including a coupling means therebetween having an effective electrical length such that the transit angle of an electromagnetic wave traversing said coupling means and that of the electrons in said beam between said resonators differs by 11' times an odd number, means communicating with said coupling means at a substantially equal distance from both said openings for introducing signal modulation of ultrahigh frequency into said resonators, and a third resonator mounted about said beam path between said first-mentioned resonator and said collector electrode for absorbing ultrahigh frequency energy from said beam.

EMILE TOURATON. RENE: ZWOBADA.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,280,824 Hansen et al Apr. 28, 1942 2,281,935 Hansen et a1. May 5, 1942 2,368,031 Llewellyn Jan. 23, 1945 2,405,611 Samuel Aug. 13, 1946 2,406,371 Hansen et a1 Aug'. 27, 1946 2,460,288 Hansen et al Feb. 1, 1949 2,464,549 Barford Mar. 15, 1949 

